Seagate ST3400755SS Signal characteristics, SAS transmitters and receivers, Power, Ready LED Out

9.4.6SAS transmitters and receivers

A typical SAS differential copper transmitter and receiver pair is shown in Figure 29. The receiver is AC cou- pling to eliminate ground shift noise.

	TX
Transmitter	Differential
	Transfer Medium
100
	TY

Figure 29. SAS transmitters and receivers

.01

.01

RX

Receiver

100

RY

9.4.7Power

The drive receives power (+5 volts and +12 volts) through the SAS device connector.

Three +12 volt pins provide power to the drive, 2 short and 1 long. The current return for the +12 volt power supply is through the common ground pins. The supply current and return current must be distributed as evenly as possible among the pins.

Three +5 volt pins provide power to the drive, 2 short and 1 long. The current return for the +5 volt power sup- ply is through the common ground pins. The supply current and return current must be distributed as evenly as possible among the pins.

Current to the drive through the long power pins may be limited by the system to reduce inrush current to the drive during hot plugging.

9.5Signal characteristics

This section describes the electrical signal characteristics of the drive’s input and output signals. See Table 10 for signal type and signal name information.

9.5.1Ready LED Out

The Ready LED Out signal is driven by the drive as indicated in Table 11.

Table 11: Ready LED Out conditions

Normal command activity		LED status
Ready LED Meaning bit mode page 19h	0		1
Spun down and no activity	Off		Off
Spun down and activity (command executing)	On		On
Spun up and no activity	On		Off
Spun up and activity (command executing)	Off		On
Spinning up or down		Blinks steadily
	(50% on and 50% off, 0.5 seconds on and off for 0.5 seconds)
Format in progress, each cylinder change		Toggles on/off

Cheetah NS SAS Product Manual, Rev. B 55